Here is sample letter inquiring the customers about their delay in repaying their overdue amount.

Name
Street Address
City, State, Zip

Dear ____ (name):

We are interested in our customers and are always trying to find new ways to improve our service. For these reasons, we are inquiring if there is a reason for your delay in paying your long overdue account. If we can help - by making your payments smaller or extending our terms or by   recommending a loan company -- please let us know. We would appreciate a word from you -- as well as your check.

Sincerely